Allogeneic bone marrow transplantation has recently emerged as a potentially curative therapeutic modality in acute and chronic leukemia. However, only a minority of leukemic patients are good-risk candidates for the procedure, and even this group has a significant complication rate. The intent of the program project is to impact fundamentally the three major causes of morbidity and mortality in transplanted leukemic patients: (1)\graft versus host disease; (2)\opportunistic infection with cytomegalovirus; and (3)\recurrent leukemia. To this end, six basic and clinical research projects will interface with each other with an active bone marrow transplantation unit. The results should facilitate the early development and clinical application of new methods for the prevention and treatment of the three principal problems associated with bone marrow transplantation in leukemic patients. (TT)